The present invention relates to electric switches, and more particularly pertains to an improved piezoelectric switch incorporating a unique system of discerning between deliberate touch activation and various other false trigger possibilities which can provide information concerning the duration of the activating contact.
Mechanical activated switches provide switch control capabilities,but are affected by environmental factors such as extreme temperature variations and moisture and are subject to degradation due to wear, which can limit such switch""s life and effectiveness. Non-mechanical, electrical switches, like piezoelectric switches, avoid the life limiting wear characteristics inherent to mechanical switches, but are subject to false activation.
The present invention provides an improved electrical switch which possesses the ability to detect the occurrence of when an object such as a human finger applies pressure to the switch and the ability to monitor the duration of the presence of such object in contact with the switch. The present invention, therefore, can provide a relatively accurate, controlled means of discerning between intentional switch actuation and anomalies which might cause unintentional activation as well as provide an accurate measure of the duration of the switch activation contact.
The present invention is broad enough to contemplate an electrical switch which monitors two separate conditions. The preferred embodiment, described in detail subsequent, monitors actuation pressure applied to the switch and capacitive change in the switch""s case caused by contact with a conductive object, such as a human finger. By requiring these separate conditions precedent, the switch avoids actuation by pressure placed upon the switch inadvertently, such as by incidental contact or by sound waves or atmospheric variations, and avoids actuation by only conductive contact with the switch, such as by contact with inadvertent liquid spills, humidity, or rain.
The present invention contemplates an electrical switch and a method of generating an electrical switch output signal. The electric switch senses both pressure placed upon the switch""s surface and the contact of the object exerting the pressure on the switch. When both conditions exist, the switch is activated. The electrical switch may employ a piezoelectric element to recognize the application of pressure, a capacitive sensing circuit to recognize the presence of an object applying the pressure, and a microcontroller circuit to control output switch circuity upon satisfaction of both conditions precedent. The electrical switch can be configured to provide a continuous output signal for the duration that the switch is pressed after the conditions are satisfied or to switch between open and closed states each time the conditions are satisfied
While the above are important features of the invention, there are, of course additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. In this respect, before explaining at least one preferred embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which the disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, or systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.